Hepatitis B virus (HBV) infection leads to a wide spectrum of liver injury varying from acute self-limited infection, fulminant hepatitis, asymptomatic healthy carrier state, to chronic hepatitis with progression to cirrhosis and liver failure. Moreover, chronic HBV infection has been linked to the subsequent development of hepatocellular carcinoma, a major cause of death from cancer worldwide. The pathogenesis of liver injury due to acute and chronic HBV infection is not well understood at present. The virus does not exert a cytopathic effect on hepatocytes; hepatotoxicity is likely a sequela of host immune responses to HBV antigens. In addition to hepatotropism, HBV infection has been associated with many other systemic immunological diseases such as polyarteritis nodosa, serum sickness-like syndrome, glomerulonephritis, and aplastic anemia. Therefore, the host immune responses to HBV-related antigens plays a major role in the pathogenesis of disease associated with HBV infection.
HBV is a partially double-stranded circular genome enclosed in a core structure surrounded by a lipid bilayer envelope containing Hepatitis B surface protein. HBV has a unique fourth open reading frame coding for a 16 kDa protein known as HBX. HBX appears to possess multiple functions. It activates a variety of viral and cellular promoters in diverse cell types (Colgrove et al., J. Virol. 63:4109-4026, 1989; Seto et al., Nature 344:72-74, 1990; Maguire et al., Science 252:842-844, 1991; Cross et al., Proc. Natl. Acad. Sci. USA 90:8078-8082, 1993), and therefore is a transactivator. Although the X protein does not bind to DNA directly, it activates transcription when it is targeted to a promoter by fusion to a heterologous DNA binding domain (Seto et al., supra; Maguire et al., supra; Cross et al., supra; Unger et al., The Eur. Mol. Biol. Org. J. 9:1889-1895, 1990). The protein has also been shown to function through AP-1 and AP-2 (Seto et al., supra) and to interact directly with members of CREB/ATF transcription factor family (Maguire et al., supra). Furthermore, a "Kunitz domain," characteristic of kunitz-type serine protease inhibitors, is present in HBX, and mutation of this consensus sequence inactivates the transactivation function of HBX (Takada et al., Jpn. J. Cancer Res. 81:1191-1194, 1990). In a transgenic mouse model, HBX has been shown to induce development of hepatocellular carcinoma (Kim et al., Nature 315:317-320, 1991). HBX also has been shown to play an essential role in HBV infection in vivo (Chen et al., J. Virol. 67:1218-1226, 1993; Zoulim et al., J. Virol. 68:2026-2030, 1994).
Eucaryotic cells contain multiple proteolytic systems, including the lysosomal proteases, calpains, the ATP-ubiquitin-proteasome-dependent pathway, and an ATP-independent nonlysosomal process. The major neutral proteolytic activity in the cytosol and nucleus is the proteasome, a 20S (700 kDa) particle with multiple peptidase activities. The function of the proteasome in vivo is not fully understood. However, the processing of protein antigens is believed to be accomplished by proteins of the proteasome complex. That is, small peptides are generated via proteolysis of large antigens, and are presented in the context of multiple histocompatibility complex (MHC) molecules to T lymphocytes to initiate an immune response.
One object of the invention is the identification and characterization of cellular targets of HBX.
Another object of the invention is to provide a novel cellular protein target of HBX.
Yet another object of the invention is to provide compounds that interfere with Hepatitis B virus infection by preventing productive interaction between HBX and a cellular protein target.